In wireless regional area networks (WRAN), the base station (BS) and associated customer premise equipment (CPE) actively detect the presence of incumbent licensed users or other WRAN systems in the operating frequency band/channel currently being used by the base station and the CPE. If licensed incumbent users are detected, the WRAN needs to switch to another channel to avoid interference with the incumbents. If other WRANs are detected, the WRAN may also switch to another channel to avoid interference between WRANs and allow WRANs to coexist in the spectrum.
A WRAN needs to stop transmitting on the channel it is currently using for operations (transmission/reception), i.e. to become quiet, in order to detect/sense whether an incumbent or another WRAN is also operating on the same channel. This results in service/operation disruption and reduction in WRAN throughput. Furthermore, this procedure introduces delay and the BS/CPE need to buffer the data during the quiet/sensing time.
In some proposals, a quiet time period is scheduled periodically. The WRAN system senses the channel at the quiet time. This approach results in service disruption. The WRAN system cannot transmit data during the quiet time. The data must be buffered at the base stations and CPEs, which introduces delay and higher buffer requirement. Delay may not be tolerable by the real-time traffic such as voice and video applications.
In another proposal, periodic channel hopping was used. In this scheme, the WRAN periodically changes its operating channel. When it hops to a new channel, channel sensing can be performed, on the old operating channel. With this approach, the WRAN operates in a channel for a fixed time before hopping to another channel. If there are multiple WRANs sharing multiple channels, this approach requires a complex scheduling scheme for channel hopping. Otherwise, two or more WRANs may hop to the same channel, which may cause a collision and interference between WRANs for the whole frequency hopping period.